I just joined another Air and the 4in1 driver detects it properly and adds the button child. It also added the button child to my existing Air after following your instructions above. The data appears to report properly right away. The only issue I had during testing was the double-click of the button. It wasn't reported as a double-click - just as a single-click. If I slowed down the double-click they appeared as individual single clicks. Hold and release work well.
@kkossev Sent you another PR to add this guy (sorry for the spam, both here and on github... feel free to tell me to stop):
It's cheap looking and almost certainly a white label, and behaves likes a PIR sensor (that's why it went here easier than your mmWave driver), but it's the cheapest battery-operated mmWave sensor I've found. And so far it seems to work (standing very still right in front of it keeps motion active). No idea what battery life will look like, but it takes 2xAAA so at least it's easy to swap.